Succeeding as an eBay seller isn't a slam dunk these days. While it's certainly easy enough to get started, the competition is stiff. Take some advice from Kevin North, CEO of Terapeak, an analytics company that provides e-commerce transactional data to more than a million merchants on eBay and Amazon. Here's his advice on how to do it right.

Don't quit your day job, yet.

It's going to take some time to figure out what works and how to compete with big retailers who have invested heavily in nailing e-commerce, so start out part-time. "As a small merchant trying to sell on eBay you're dealing with competitors that you didn't have to deal with five to ten years ago," he says. "And eBay itself is a wonderful marketplace, but you have to know what you're doing to be successful."

Sell products you're passionate and knowledgeable about.

And start small. "Don't overly diversify, especially early on, because you don't want to get into situation where you're stuck with inventory that you can't move, because that happens to a lot of people," he says. "Before you go big just find something you're passionate about, keep it to a very particular, specific niche, and then work out from there."

Find out what's selling well, at what prices and in what countries.

Yes, it's biased advice considering Terapeak sells this information starting at $15 a month, but you can be sure the e-commerce behemoths you're up against are mining this data. For example, maybe you want to sell widgets, not knowing either they won't sell, or they're the most saturated item on the platform, meaning you'd be up against countless other merchants. "But maybe if you go into an adjacent product line, the sky is gold," he says.

Optimize your listings.

If you don't use the right key words, descriptions, colors and images you're never going to get buyers to find your items and click on them. "In a world where there's millions of listings often on a single product... those things are very important in being found," he says. Terapeak offers a free product, MySales, that will analyze a merchant's sales across channels and will score and improve their eBay listings.

Understand your sourcing options.

You can bet the most competitive merchants on eBay are using global suppliers, often from China. But how do you go about doing so? North suggests using Global Sources and Alibaba which provide sourcing advice and lists of verified sources as well as ones to avoid. "The best sellers on eBay will have invested in their sourcing process," he says.